guest ::
| Home > Publications database > Femtosecond electron dynamics of image-potential states on the transition-metal surfaces of Pt and Ni |
| Home > Publications database > Femtosecond electron dynamics of image-potential states on the transition-metal surfaces of Pt and Ni |
| Dissertation / PhD Thesis/Book | PreJuSER-24995 |
2001
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/19981
Report No.: Juel-3878
Abstract: The influence of the electronic structure upon the relaxation dynamics of optically excited electrons has been investigated on the transition metal surfaces of Pt and Ni . Using time-resolved two-photon photoemission spectroscopy the population dynamics of excited electronic states can be observed. It was the purpose of this thesis to extract the influence of d-band and surface-state contributions onto the dynamis and lifetimes of so called "image-potential states" . Image-potential states are a special class of bound, normally unoccupied, electronic surface states. They are localized in the vacuum region in front of a metal surface and energetically converge - similar to the Rydberg series of a hydrogen atom - with quantum number n towards the vacuum energy. It has been demonstrated that changes in the surface geometry caused by adsorbates influence the lifetimes of those states, which typically lie in the femtosecond range. Our experiments show that the lifetimes of image states can be both lowered and increased depending on the the sort of atoms adsorbed at the surface. Therefore, it is possible to control lifetimes of surface states on ultrashort time scales . In particular, we have investigated the first two image-potential states on the Pt(111) surface as well as the first state (n = 1) on the (111) and (100) orientations of Ni. On Pt(111), lifetimes of 26 ± 7 and 62 f 10 fs have been measured for the first two image states, respectively. The adsorption of a quarter of a monolayer leads to a reduced lifetime for both states by a factor of 2. This decrease can be explained by the redistribution of the density of states close below the Fermi energy. The observed lifetimes of < 20 fs for the first image-potential state on Ni(100) and Ni(111) are significantly shorter compared to those on Pd, Pt and the noble metals Cu and Ag. This can be essentially attributed to the high density of states of d-bands at the Fermi level, which contribute to the population decay. In order to understand the lifetimes of image-potential states on the transition and noble metal surfaces, a model has been developed which is able to describe the observed lifetimes reasonably well and allows to predict up to now unmeasured lifetimes.
|
The record appears in these collections: |
PDF
PDF (PDFA)